1. Field of the Invention
The present invention relates to a multiplex connection inverter apparatus having a plurality of inverters connected for multiplexing and particularly to a multiplex connection inverter apparatus adapted for minimizing undesired current ripples generated when the alternative current outputs of inverters with carrier signal components of the alternating current outputs are superposed in phase with each other.
2. Description of the Related Art
A common PWM inverter apparatus comprises a converter unit for converting alternating current receiving from an alternating current generator or power source into direct current and an inverter unit for re-converting a direct current output of the converter unit into an alternating current output having a desired frequency. Such a PWM inverter apparatus is disclosed in Japanese Patent Laid-open Publication (Showa) 60-98875 which has a group of PWM inverters multiplex connected for producing high-power alternating current outputs at desired frequencies through PWM controlling the switching elements (e.g. power transistors) of the inverters with a PWM signal which consists of a waveform command such as a voltage or frequency control command and a carrier signal.
The alternating current output of each PWM inverter controlled by PWM signal contains a carrier signal component used for generation of the PWM signal, as shown in FIG. 8. If the alternating current outputs are simply superposed while their carrier signal components are in phase with each other, their carrier signal components can significantly be amplified as shown in FIG. 9. As a result, voltage ripples in the alternating current output will unfavorably be increased.
It is hence an object of the present invention to minimize current ripples generated when the alternating current outputs of inverters with carrier signal components of the alternating current outputs are superposed in phase with each other.
A multiplex connection inverter apparatus according to the present invention is provided which has a pair of inverters arranged for superposing their alternating current outputs. In particular, the alternating current outputs are superposed with their carrier signal components held opposite in the phase to each other.
According to the above advantage of the present invention, the alternating current outputs of the inverters are multiplexed while their carrier signal components are offset by each other, thus decreasing undesired current ripples.